Demand for white LEDs (Light Emitting Diodes) is rapidly increasing as white light sources for cell phone LCD (Liquid Crystal Display) parts, LCD televisions, and lighting fixtures. A white LED is based on an LED for emitting blue light or ultraviolet light. On the other hand, semiconductor lasers for emitting blue light or ultraviolet light are used in such applications as pickup light sources for reading and writing high-density optical discs and automotive headlamps. Furthermore, HEMTs (High Electron Mobility Transistors) are used as high-power semiconductor devices for motor control in cars and trains. These LEDs, semiconductor lasers, and HEMTs are formed by crystal growth of a nitride semiconductor made of InyAlzGa1-y-zN (0<y≦1, 0≦z≦1) on a sapphire or other substrate. Crystal defects in a nitride semiconductor decrease the internal quantum efficiency of the light emitting device such as LED and semiconductor laser. Furthermore, crystal defects accelerate the degradation of the light emitting device and impair its reliability. In electron devices such as HEMT, crystal defects decrease the electron mobility and lead to power loss. In order to reduce crystal defects in the nitride semiconductor layer made of InyAlzGa1-y-zN to improve the light emission efficiency and reliability of the light emitting device, the nitride semiconductor layer made of InyAlzGa1-y-zN is formed on a sapphire substrate with a pattern of depressions and protrusions formed on the substrate surface.